The present invention relates to dual band, coplanar antennas. In particular, the present invention relates to dual band coplanar antennas having interlaced arrays to minimize the surface area required by the antenna.
Antennas are used to radiate and receive radio frequency signals. The transmission and reception of radio frequency signals is useful in a broad range of activities. For instance, radio wave communication systems are desirable where communications are transmitted over large distances. In addition, radio frequency signals can be used in connection with obtaining geographic position information.
In order to provide desired gain and directional characteristics, the dimensions and geometry of an antenna are typically such that the antenna is useful only within a relatively narrow band of frequencies. It is often desirable to provide an antenna capable of operating at more than one range of frequencies. However, such broadband antennas typically have less desirable gain characteristics than antennas that are designed solely for use at a narrow band of frequencies. Therefore, in order to provide acceptable gain at a variety of frequency bands, devices have been provided with multiple antennas. Although such an approach is capable of providing high gain at multiple frequencies, the provision of multiple antennas requires relatively large amounts of physical space.
An example of a device in which relatively high levels of gain at multiple frequencies and a small antenna area are desirable are wireless telephones capable of operating in connection with different wireless communication technologies. In particular, it may be desirable to provide a wireless telephone capable of operating in connection with different wireless systems having different frequencies, when communication using a preferred system is not available. Furthermore, in wireless telephones, a typical requirement is that the telephone provide high gain, in order to allow the physical size and power consumption requirements of the telephone components to be small.
Another example of a device in which high gain characteristics at multiple frequencies and a small antenna area are desirable are global positioning system (GPS) receivers. In particular, GPS receivers using dual frequency technologies, or using differential GPS techniques, must be capable of receiving weak signals transmitted on two different carrier signals. As in the example of wireless telephones, it is generally desirable to provide GPS receivers that are physically small, and that have relatively low power consumption requirements.
Still another example of a device in which a relatively high gain at multiple frequency bands is desirable is in connection with a communications satellite or a global positioning system satellite. In such applications, it can be advantageous to provide phased array antennas capable of providing multiple operating frequencies and of directing their beam towards a particular area of the Earth. In addition, it can be advantageous to provide such capabilities in a minimal area, to avoid the need for large and complex radiator structures.
Planar microstrip antennas have been utilized in connection with various devices. However, providing multiple frequency capabilities typically requires that the area devoted to the antenna double (i.e., two separate antennas must be provided) as compared to a single frequency antenna. Alternatively, microstrip antenna elements optimized for operation at a first frequency have been positioned in a plane overlaying a plane containing microstrip antenna elements adapted for operation at a second frequency. Although such devices are capable of providing multiple frequency capabilities, they require relatively large surfaces or volumes, and are therefore disadvantageous when used in connection with portable devices. In addition, such arrangements can be expensive to manufacture, and can have undesirable interference and gain characteristics.
The amount of space required by an antenna is particularly apparent in connection with phased array antennas. Phased array antennas typically include a number of radiator elements arrayed in a plane. The elements can be provided with differentially delayed versions of a signal, to steer the beam of the antenna. The steering, or scanning, of an antenna""s beam is useful in applications in which it is desirable to point the beam of the antenna in a particular direction, such as where a radio communications link is established between two points, or where information regarding the direction of a target object is desired. The elements comprising phased array antennas usually must be spread over a relatively large area. Furthermore, in order to provide phased array antennas capable of operating at two different frequency bands, two separate arrays must be provided. Therefore, a conventional phased array antenna for operation at two different frequency bands can require twice the area of a single frequency band array antenna, and the phase centers of the separate arrays are not co-located. Alternatively, arrays can be stacked one on top of the other, however this approach results in antennas that are difficult to design such that they operate efficiently, and are expensive to manufacture. In addition, prior attempts at providing antenna arrays capable of operating at two distinct frequency bands have resulted in poor performance, including the creation of grating lobes, large amounts of coupling, large losses, and have required relatively large areas.
Therefore, there is a need for an antenna capable of operating at multiple frequencies that is relatively compact and that occupies a relatively small surface area. In addition, there is a need for such an antenna capable of providing a beam having high gain at multiple frequencies that can be scanned. Moreover, there is a need for an antenna capable of providing high gain at multiple frequencies that can be packaged within a relatively small area or volume, and that minimizes coupling and losses due to the close proximity of the antenna elements. Furthermore, it would be advantageous to provide an antenna capable of operating at multiple frequency bands and having co-located phase centers. In addition, such an antenna should be reliable and inexpensive to manufacture.
In accordance with the present invention, a dual band, coplanar, microstrip, interlaced array antenna is provided. The antenna includes a first plurality of antenna radiator elements forming a first array for operation at a first center frequency, interlaced with a second plurality of antenna radiator elements forming a second array for operation at a second center frequency. The antenna is capable of providing high gain in both the first and second center frequencies. In addition, the antenna may be designed to provide a desired scan range for each of the operating frequency bands.
In accordance with an embodiment of the present invention, the first and second pluralities of antenna radiator elements are located within a common plane. In addition, radiator elements adapted for use in connection with the first operating frequency band may be interlaced with radiator elements adapted for operation at the second operating frequency band. Accordingly, the footprint or area of the first antenna array may substantially overlap with the footprint or area of the second antenna array. Therefore, a dual band array antenna may be provided within an area about equal to the area of a single band array antenna having comparable performance at one of the operating frequencies of the dual band antenna.
In accordance with an embodiment of the present invention, a dual band, coplanar, microstrip array antenna is formed using metallic radiator elements. Radiator elements for operation at a first operating frequency band of the antenna are provided in a first size, and overlay a substrate having a first dielectric constant. Radiator elements for operation in connection with the second operating frequency band of the antenna are provided in a second size, and are positioned over a substrate having a second dielectric constant. The radiator elements may be arranged in separate rectangular lattice formations to form first and second arrays. The elements of the first and second arrays are interlaced so that the resulting dual band antenna occupies less area than the total area of the first and second arrays would occupy were their respective radiator elements not interlaced.
In accordance with still another embodiment of the present invention, a method for providing a dual frequency band antenna apparatus is provided. According to such a method, first and second center frequencies are selected. In addition, a scan range for the first center frequency and a scan range for the second center frequency are selected. From the wavelength corresponding to the first center frequency and the scan range for that first center frequency a lattice spacing for a first plurality of radiator elements is determined. The lattice spacing is the center to center spacing between radiator elements within an array of elements. Similarly, a lattice spacing for a second plurality of radiator elements is determined from the wavelength corresponding to the second center frequency and the scan range for the second center frequency. The maximum lattice spacing is the smaller of the lattice spacings for the first or second plurality of radiator elements. Where the scan range of one or both arrays is a first value in a first dimension and a second value in a second dimension, lattice spacing calculations may be made for each dimension.
A dielectric constant for a first substrate as a function of the wavelength of the first center frequency and the maximum lattice spacing may then be selected. The dielectric constant for the first substrate should have a value that is no less than 1.0. The dielectric constant for a second substrate may then be calculated as a function of the first substrate dielectric constant, the first center frequency, and the second center frequency. Next, an effective size of the radiator elements in the first plurality of radiator elements and of the radiator elements in the second plurality of radiator elements can be calculated as a function of the wavelength of the operative center frequency and the corresponding dielectric constant of the substrate. A physical size of the first radiator elements and of the second radiator elements can then be calculated.
In accordance with a further embodiment of the present invention, a first plurality of radiator elements are formed on dielectric material having a dielectric constant equal to the first dielectric constant calculated according to the method. In addition, the second plurality of radiator elements is formed on dielectric material having a dielectric constant equal to the second dielectric constant. A first array may then be formed from the first plurality of radiator elements. The radiator elements of the first array are arranged about a rectangular lattice and have a center to center spacing equal to the calculated maximum lattice spacing. Similarly, a second array is formed from the second plurality of radiator elements. The radiator elements of the second array are arranged about a rectangular lattice and have a center to center spacing equal to the calculated maximum lattice spacing. The first array is then interlaced with the second array. Accordingly, a dual band antenna occupying a reduced surface area may be provided.
In accordance with another embodiment of the present invention, a method for modifying the effective dielectric constant of a material is provided. According to the method, portions of a material may be relieved, for example by forming holes in the material, in an area in which a modified (i.e. reduced) dielectric constant is desired. According to an embodiment of the present invention, a modified effective dielectric constant is obtained by forming holes in a triangular lattice pattern in an area of a dielectric material in which a reduced effective dielectric constant is desired. In accordance with yet another embodiment of the present invention, a material having a modified effective dielectric constant is provided.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. A dual band antenna that allows for the scanning of the two center frequencies is provided. The antenna further allows for the provision of a dual band scanning antenna apparatus occupying a reduced surface area. The antenna allows support of both center frequencies with minimal or no grating lobes and minimal coupling. The antenna may be formed from two, co-planar, interlaced arrays. Furthermore, the present invention allows the provision of a dual band scanning antenna that occupies a reduced surface area, that provides a desired scan range of the operative frequencies and in which a desired amount of directivity is provided.
In addition, a material having a modified effective dielectric constant, and a method for modifying the effective dielectric constant of a material, are provided.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.